RF splitter modules are commonly used in fields of application such as CATV (community antenna television) distribution systems, in which a single RF antenna and input is used for multiple purposes. A typical such application is shown in FIG. 1, which depicts an example RF front-end of a DVD-R (Digital Video Disk Recorder) system. The RF front end comprises a RF input 1 which is connected to RF output 2 and 3 by means of amplifiers A and B respectively. Bypass switch 4 is connected in parallel with amplifier B, in order to provide a switchable bypass route for bypassing amplifier B. Thus output 2 forms the RF output for the device tuner, whilst output 3 provides an RF loop-through output. The bypass switch enable the output 3 to be an amplified version of the signal at input 2, or a copy of the input. In the latter instance, it is preferred that the output copy suffers little or no degradation with respect to the input.
Other example applications which require a similar RF splitter include multi-tuner cable set-top boxes, cable splitter modules, multi-tuner televisions, and home gateways. Conventionally, a discreet passive splitter is used followed by separate fixed gain amplifiers, although it would in many instances be preferable to include an RF switch in order to bypass an amplifier or attenuator
In FIG. 1, the outputs have been shown as tuner output, and loop-through output. However in different applications, the created output paths may include such diverse modules as main picture tuners, picture-in-picture (PIP) tuners, digital video recorder (DVD-R), and cable modems (CM).
In the prior art, switch 4 typically comprises a depletion mode MOSFET which is introduced into the splitter module as a separate, or external, component. An example of such a MOSFET which is suitable for this application is the device BF1108 silicon RF switch supplied by NXP Semiconductors; other similar such low-loss RF switching MOSFETs are also available.
The presence of such an external switch requires that power is supplied to the splitter device. However, it is desirable that when the device is in standby mode, the power consumption is minimised. There is thus an ongoing need for an RF switch which forms part of an RF splitter device, which consumes little or no power when the device is in standby mode, but still provides a bypass function.